Silver halide photographic materials currently on the market and methods for forming images using the same vary over a wide range and are used in various fields. Many of the halide compositions of silver halide emulsions used in many of these photographic materials, in particular in the case of shooting photographic materials, consist of silver bromoiodide that is mainly made up of silver bromide, for the purpose of attaining high sensitivity.
On the other hand, in products that are used in a market where there is strong demand for a large amount of prints to be finished and delivered in a short period of time, such as photographic materials for color papers, silver bromide or silver chlorobromide that is substantially free from silver iodide is used, in order to hasten the developing speed.
In recent years the demand for the improvement of rapid processibility of color papers has been increasingly strong and many studies thereof are under way. It is known that an increase in the silver chloride content of the silver halide emulsion to be used will greatly improve developing speed.
However, it is known that silver halide emulsions high in silver chloride content are attended with such defects that they hardly provide emulsions high in sensitivity and hard in gradation. Further the emulsions have a defect that reciprocity law failure, that is, the change of sensitivity and gradation due to a change in illuminance of exposure is great.
In order to overcome the above defects of silver halide emulsions high in silver chloride content, various techniques have been proposed.
JP-A ("JP-A" means unexamined published Japanese patent application) No. 26837/1989 discloses that a high-silver-chloride emulsion, whose grains have regions rich in silver bromide near the vertices gives high sensitivity and gradation and stable performance. JP-A No. 105940/1989 discloses that a high-silver-chloride emulsion having regions rich in silver bromide doped selectively with iridium constitutes an emulsion excellent in reciprocity response without damaging latent-image stability for a few hours after exposure.
Further, the inventors have continued to engage keenly in studies to increase greatly the performance of high-silver-chloride emulsions. As a result, it has become apparent that when a high-silver-chloride emulsion prepared in the above manner is used for a photographic material and the photographic material is exposed to safelight before printing, the gradation becomes inevitably softened and the latent-image stability over a longer period of time, that is, a few days after printing, is not necessarily satisfactory. If this happens the photographic material not only lacks handleability in photofinishing laboratories, the quality of the finished print will also drop.
The inventors have found that when a high-silver-chloride emulsion is sensitized with gold, latent-image stability over a longer period of time can be considerably improved. However, sometimes the use of gold sensitization brings about a softening of gradation or worsens the aging stabilities of emulsion before application and photographic material, and therefore gold sensitization could not make adequate use of the above merits of high-silver-chloride emulsions.